Process for preparing photographic elements



United States Patent Robert. Herrma nn Franke and Humphrey Desmond Murray, London, England, assignors to Ozalid Company Limited, London, England, a Brifish company Application September 4, 1952, Serial No. 307,898

Claims priority, application Great Britain September 11, 1951 No Drawing.

;The-present invention relates to diazotype materials and coating compositions therefor, and more particularly togdiazotype. materials of the type known as dry developed materials which may be developed by moist alkaline vapours.

It is known to sensitise cellulose acetate films, and cellulose acetate lacquers applied to paper and other bases, by means of solutions containing light sensitive diazo compounds. Sensitization can be effected by partially saponifying the surface of the film or lacquer by inaeans of alkaline solutions and, after washing, coating the partially saponified surface with an aqueous solution of the sensitizing substances. Alternatively, sensitizae ftion can be effected by applying to the surface of the film or lacquer a solution of thesensitizing substance in 1a, solvent which swells the surface of the cellulose acetate.

The first method involves the preliminary step of partially saponifying the surface to be coated. In practice it is found di'ificultto control the degree of saponification, and the operation of the saponifying process addstothe costof manufacture of the finished product.

The second method involves the use, in specially adapted coating machines, of solvents such as alcohol or acetone, the vapours of which are inflammable, or of chlorinated solvents, the vapours of which are toxic.

One object of the present invention is to provide a method of sensitizing paper or otherbase with a lacquer containing a light sensitive diazotype-composition in one operation and without theme of inflammable or toxic solvents. t a

- Afurther objectof the present invention is to provide a* lacquer coating which is permeable to. gases and vapoursabut impermeable to. water, thus yielding water- 'proofimages. 1

A thirdobj'ecnoftheipresent invention is to :provide a sensitized lacquer coating yielding images of high contrast-r" I 3 It has been found that aqueous emulsions of certain synthetic: resins can be. prepared in a form compatible acidic diazotype compositions. sions produce on drying, lacquer coatings having the aboveproperties and also: the property of breaking during drying, whereby the synthetic resin previously dispersed in: an; aqueous: phase. is. left as. a continuous film upon other base which process comprises mixing an aqueous emulsion of a polyvinyl compound partly polymerised to a stage where the resin droplets are still liquid, stabilized against electrolyte precipitation and having the property of breaking while drying to give a continuous film which can be further polymerised by heating, to produce a water insoluble lacquer permeable in thin layers to ammonia vapour with a diazotype sensitizing solution, comprising a light sensitive diazo compound, a coupling component, and a fixed acid, coating the mixture onto paper or other base, drying, whereby the emulsion mixture breaks and heating so as to further polymerise the resin film.

Preferably the base is pre-treated with an aqueous sizing emulsion of polyvinyl compound before the. light sensitive coating emulsion is applied. I

The aqueousemulsions are prepared from vinyl compounds which have been emulsified and partly polymerised to a stage where the resin droplets are still liquid so that on drying the emulsion is capable of forming a continuous film. If polymerisation is taken too far such film formation does not take place. It is essential, therefore, that the vinyl compounds in the emulsion should be only partly polymerised.

The vinyl compounds which We have found to be suitable are vinyl chloride, vinyl acetate, vinyl acetal, styrene, acrylates and methacrylates.

Emulsions may be formed of the above substances in pure form or as :co-polymcrs onewwith another. Alternatively, emulsions of one or other of the above may be prepared and mixed before using.

In use it is essential that the concentration of the solid resin in the mixture prepared forcoating shall be suflicient to form a film as the mixture dries. It the concentrationyof resin is too low, no continuous film forms on drying but isolated aggregates of the resin remain upon the surface.

The hardness of the films formed on drying depend upon the nature of thepolymer or of the co-polymers employed in the emulsion, thus methyl methacrylate resins tend to give hard coatings and proportions thereof may be mixed with other resins to increase the hardness of the resultant film.

It would appear that. the ability oli ammonia vapour to penetrate into the resin film so as to ensure-development of the light sensitive mixture is dependent upon the presence in the resin of the linkage CH2= CH The Such emulthe coated base. The light sensitive diazo-compound a'nd the coupling component previously dissolved in the aqueous phase are left dissolved or dispersed inthe dried lacquer The final product i-sa base with a waterproof surface, capable. of yielding prints (after exposur e to light beneath a tracing and development in men vapour) of high visual contrast.

; ccordihg to the present invention there isproxided a. procession coating paper or other wettable; base with a, water insoluble gas permeable. light. sensitive diazotype lacquer capable of dry development on the: paper; or

rate of penetration of ammonia may be improvedby the presence in the sensitising mixture of" water soluble plasticizers such as. polyethylene glycol and derivatives thereof. i a In the preparation of emulsion mixtures it is essential to avoid the presence in the mixture ofsubstancessuch as large concentrations of water soluble gums or other hydrophilic colloids which become still further concentrated on drying. of the emulsion-and prevent the liquid resin droplets from coalescing so. as. to form a contimqous film. The choice of diazo compounds and of coupling components is restricted to those substances which are compatible with the stabilized resin emulsiongandare soluble in or dispersible in the droplets of the emulsiom so that on drying the emulsion breaks to form.a continuous film carrying the diazo compound and tlie coupling component. i We have found that among suitable diazo compounds are the diazonium chlorides derivedfrom para-diinethyl amino aniline, para diethyl amino aniline, and para hyr droxyetl-ryl ethyl amino aniline or; their double salts, with zinc chloride and para-diazo diphenylamine sulphat Among suitable coupling components are"2,3- dihy droxy naphthalene, 6-sulphonic acid, phloroglucinol, te-

sorcinol, aceto-acetic anilide, and the urea of meta amino phenol.

When resin emulsions containing diazo compounds and azo coupling components are coated directly upon an unlacquered paper base, it is desirable to add to the mixture substances such as water soluble metallic salts, e. g. zinc chloride or aluminium sulphate, which reduce the solubility in water of the diazo compound and of the coupling components.

Before adding the sensitising chemicals to the resin emulsion, the latter must be stabilized against electrolyte precipitation. Such stabilized emulsions of polyvinyl acetate and polyvinyl chloride are obtainable commercially.

We have found that an emulsion of polyvinyl acetate may be stabilized against electrolyte precipitation, by adding to the emulsion polyvinyl alcohol, and ethylene glycol, or a derivative thereof and mixing with a high speed stirrer.

Substances known in the art which stabilize diazotype coatings and prevent discolouration of the background of developed prints may be included in the coating emulsion, together with plasticizers and small quantities of dyestuffs to improve the colour of the background of prints. For example an anhydrous condensation product of a long chain fatty alcohol and ethylene oxide may be employed as a stabiliser.

Following is a description by way of example of methods of carrying the invention into effect:

Solution A is filtered and run with stirring into emulsion B. The mixture is then coated on a base in known manner by dipping, spraying or by means of rollers.

In the case of paper or other absorbent base, it is preferable to treat the surface before sensitizing with a sizing solution made up as follows:

A stable polyvinyl acetate emulsion ccs 210 Dibutyl phthalate (ca 10 Polyvinyl alcohol em 6 A wetting agent such as the sodium salt of a higher alkyl sulphate gm Distilled water res 500 The paper is dried and then sensitized as above.

In place of dibutyl phthalate an equal quantity of polyethyllene glycol or a water soluble ester thereof may be use Prints made by exposing the sensitized material beneath the tracing and development with ammonia vapours show bright blue lines having excellent sharpness and contrast on a white background. No bleeding of the lines occurs when the surfaces of the prints are washed with water.

Water to 500 ccs.

This is filtered and run with stirring into an emulsion made up as for emulsion B in Example 1. The mixture may be coated on a paper base sized as in Example 1 with emulsion C. Prints made from bases sensitized as above, after exposure and development with ammonia, show black lines with good sharpness and contrast, and good fastness to water, on a white background.

Example 3 A solution is prepared as follows:

A Tartaric acid gm 30 Boric acid gm 30 Naphthalene trisulphonic acid (sodium salt) gm 40 Thiourea gm 40 2-naphthol-3:6-disulphonic acid (sodium salt) gm 35 Urea of m-aminophenol "gm..- 8 P-diazodiphenylamine sulphate gm-.. 24 Glycerine "ccs-- 50 Water to 500 ccs.

This is filtered and run with stirring into an emulsion made up as for emulsion B in Example 1. The mixture may be coated on a paper base sized as in Example 1 with emulsion C. Prints made from bases sensitized as above,

after exposure and development with ammonia, show blue black lines with good sharpness and contrast and good fastness to water, on a white background.

We claim:

1. A process for preparing photographic elements comprising coating a support with a stabilised .aqueous emulsion comprising a vinyl compound, partly polymerised to a stage where the resin droplets are still liquid and selected from the group consisting of vinyl chloride, vinyl acetate, vinyl acetal, styrene, acrylates, methacrylates and copolymers thereof, a diazo type sensitizing solution comprising a light sensitive diazo compound, a coupling component and a fixed acid, drying the emulsion on the support and thereafter heating the coated support.

2. A process according to claim 1 wherein the support comprises a paper base.

3. A process according to claim 1 wherein the coupling component comprises the sodium salt of 2:3-dihydroxynaphthalene-G-sulphonic acid. 7

4. A process according to claim 1 wherein thediazo compound is a diazonium chloride.

5. A process according to claim 1 wherein the aqueous emulsion includes zinc chloride.

6. A process according to claim 1 wherein the aqueous emulsion includes polyvinyl alcohol.

References Cited in the file of this patent UNITED STATES PATENTS 2,197,456 Poser Apr. 16, 1940 2,397,866 McQueen Apr. 2, 1946 2,405,523 Sease et al. Aug. 6, 1946 2,534,326 Weaver Dec. 19, 1950 2,542,560 Neumann Feb. 20, 1951 2,551,133 Jennings et al May 1, 1951 

1. A PROCESS FOR PREPARING PHOTOGRAPHIC ELEMENTS COMPRISING COATING A SUPPORT WITH A STABILISED AQUEOUS EMULSION COMPRISING A VINYL COMPOUND, PARTLY POLYMERISED TO A STAGE WHERE THE RESIN DROPLETS ARE STILL LIQUID AND SELECTED FROM THE GROUP CONSISTING OF VINYL CHLORIDE, VINYL ACETATE, VINYL ACETAL, STYRENE, ACRYLATES, METHACRYLATES AND COPOLYMERS THEREOF, A DIAZO TYPE SENSITIZING SOLUTION COMPRISING A LIGHT SENSITIVE DIAZO COMPOUND, A COUPLING COMPONENT AND A FIXED ACID, DRYING THE EMULSION ON THE SUPPORT AND THEREAFTER HEATING THE COATED SUPPORT. 